There has been known, for a long time, a premix or a raw material for use in the preparation of TOFU at each home and some of them will be introduced herein. For instance, an example thereof is a method for preparing TOFU capable of easily released from a container for coagulation, which comprising the steps of adding water to powdered soybean milk, then heating the resulting mixture, adding a coagulating agent thereto and packaging the mixture in a container to thus solidify the same and to thereby form TOFU (see Patent Document 1 specified below). This Patent Document likewise discloses that a surfactant having an HLB value of not less than 11 is useful for the improvement of the releasability of the resulting TOFU from the container and it discloses sucrose fatty acid esters as specific examples of the surfactants.
In addition, there have also been known such disclosure as to a raw composition for preparing TOFU, which is quite excellent in the solubility and dispersibility in hot water and which permits the preparation of TOFU having stable quality according to a simple method and a method for preparing the raw composition, as well as a simple method for preparing TOFU which makes use of the raw composition for preparing TOFU (see Patent Document 2 specified below).
Moreover, there has been disclosed a raw material for preparing TOFU characterized by combining packaged TOFU which comprises a predetermined amount of sterilized soybean milk air-tightly packed in a container and a packed coagulating agent in an amount corresponding to that of the packaged TOFU and there has also been included a description concerning the preparation of, in addition to the liquid soybean milk, powdered soybean milk according to, for instance, a method comprising the steps of spray-drying, freeze-drying and/or vacuum drying such soybean milk (see Patent Document 3 specified below).
There has also been disclosed a TOFU set for the hand-fabrication thereof, which comprises separately packaging soybean milk as a raw material for forming TOFU, and a coagulating agent for solidifying the soybean milk in an amount sufficient for solidifying the same and accommodating these separate packages in the same box so that they can simultaneously be distributed (see Patent Document 4 specified below).
However, the liquid soybean milk is very liable to cause taste change during storing the same and the storage stability thereof is thus considerably reduced. Contrary to this, in case of the liquid soybean milk, which has been subjected to cruel heating and sterilization treatments during its production step for the improvement of the storage stability thereof, the protein components present therein may undergo denaturation and this in turn results in the considerable reduction of the ability of forming TOFU through coagulation. Moreover, in case of powdered TOFU, the storability thereof is improved, but the protein components thereof may undergo denaturation through the heat-treatment of soybean milk depending on the spray-drying conditions and this may result in the reduction of the ability of coagulating into TOFU. Furthermore, in case of the powdered soybean milk prepared by the freeze-drying technique, a problem arises such that the formation of such powder requires great expense.
Then there has already been known a raw material comprising powdery soybean used for preparing TOFU in each home and accordingly, some techniques for preparing the same will be herein introduced.
First of all, there has been disclosed soybean milk, or soybean powder used for preparing TOFU, which is a pulverized product of dried whole soybeans, has a 50% cumulative particle size starting from the minimum particle size (median particle size) of not more than 40 μm and a water content of not less than 5.2% as determined in terms of the weight loss observed when heating at 90° C. for 1.5 hours (see Patent Document 5 specified below).
In case of this technique, when preparing soybean milk or TOFU in each home using the foregoing pulverized product of dried whole soybeans, it is necessary to blend the pulverized product of soybeans with water and then heated, but the foregoing pulverized product of dried whole soybeans is liable to cause integration or agglomeration and to thus form agglomerates when blending it with water and heating, this sometimes leads to insufficient and non-uniform distribution of the pulverized product in hot water and a part thereof remains undissolved. As a result, the soybean milk or TOFU ultimately obtained often has unacceptable or bad appearance and is rough and unpleasant to the teeth, because of the presence of such pulverized product of the dried whole soybeans remaining therein undissolved condition.
Furthermore, there has been described a good formed into a set which is obtained by heat-treating, with stirring, soybean finely pulverized into powder having a classified average particle size of not greater than 50 μm while blowing high temperature water vapor into the same, packing up the resulting mixture and separately packing a coagulating agent, in which the mixture is blended with the coagulating agent, for instance, at each home to thus coagulate the same and to thus form TOFU of whole soybean (see Patent Document 6 specified below).
According to this method, however, the good in the form of a set is liable to undergo taste and texture changes during storage or the storage stability of the good is considerably reduced since the good includes a mixed liquid containing finely pulverized soybean powder and water. Contrary to this, such a good, which has been subjected to cruel heating and sterilization treatments during its production step for the improvement of the storage stability thereof, an additional problem may arise such that the protein components present therein may undergo denaturation and that the ability of forming TOFU through coagulation is thus considerably impaired or reduced.
Moreover, as an example of the technique for improving the dispersibility of soybean powder in water while making use of dextrin, there has been disclosed a method comprising the steps of spraying soybean protein powder with dextrin having a DE value ranging from 10 to 25 to thus give a powdery soybean protein-containing material which has an excellent solubility in water even when the material combined with water is weakly stirred, while maintaining a sufficient gel-forming ability (see Patent Document 7 specified below).
However, this method requires the steps for dissolving dextrin in water, and spraying the soybean protein powder with a shaping liquid (a binder solution) and this makes the production process quite complicated since the method requires the use of an apparatus, for instance, a fluidized bed dryer. In addition, if the dextrin used has a high DE value, the resulting product may sometimes develop the sweetness originated from the dextrin in proportion to the added amount thereof.    Patent Document 1: JP-A-Sho 49-25149;    Patent Document 2: JP-A-Sho 54-86648;    Patent Document 3: JP-A-2002-218934;    Patent Document 4: JP-A-Hei 11-346699;    Patent Document 5: JP-A-2003-189811;    Patent Document 6: JP-A-Hei 9-234010;    Patent Document 7: WO 2003/22069.